KR102168841B1 - Surface-treated steel sheet and manufacturing method of surface-treated steel sheet - Google Patents

Abstract

A surface-treated steel sheet having a film having good adhesion to an adhesive on its surface and having excellent corrosion resistance, and a method for producing the same are provided. A surface-treated steel sheet having a steel sheet, a plating layer including zinc formed on the steel sheet, and a film formed on the plating layer is provided. The film contains acrylic resin, zirconium, vanadium, phosphorus and cobalt, and the area ratio of the acrylic resin is 80 to 100 area% in a region from the surface in the cross section of the film to a thickness of 1/5 of the film thickness, The area ratio of the acrylic resin is 5 to 50 areas in a region consisting of a region from the film thickness center to the surface side to a thickness of 1/10 and a film thickness center to the plating layer side to a thickness of 1/10 %to be.

Description

Surface-treated steel sheet and manufacturing method of surface-treated steel sheet

The present invention relates to a surface-treated steel sheet having a film on its surface and a method for producing a surface-treated steel sheet.

Conventionally, plated steel sheets containing zinc are used in various fields such as home appliances, building materials, and automobiles. Further, as a method of improving the corrosion resistance of a plated steel sheet containing zinc, a technique of forming a film on the surface of a steel plate containing zinc plating is widely used (for example, see Patent Documents 1 to 3).

Japanese Patent Publication No. 2003-055777 Japanese Patent Publication No. 2005-097733 International Publication No. 2009/116484

However, even if the conventional coating formed on the surface of a zinc-containing plated steel sheet can improve corrosion resistance, there is a problem that adhesion with an adhesive is not sufficient.

An object of the present invention is to provide a surface-treated steel sheet having a good adhesion to an adhesive on its surface and having excellent corrosion resistance, and a method for producing the same.

In order to solve the above problems, the present inventors have studied intensively.

As a result, on the plated steel sheet containing zinc, the area ratio of the acrylic resin in the region from the surface to the thickness of 1/5 of the film thickness in the cross section of the film containing acrylic resin, zirconium, vanadium, phosphorus and cobalt Acrylic in a region consisting of 80 to 100% by area, from the center of the film thickness to the thickness of 1/10 to the surface side, and from the center of the film thickness to the thickness of 1/10 to the plating layer side. It was found that by forming a film having a resin area ratio of 5 to 50 area%, a film having good adhesion to an adhesive and excellent corrosion resistance could be obtained.

In addition, the film on the steel plate has a plurality of island-like projections on its surface, and has a length of 10 μm or more and extends in an arbitrary direction at an arbitrary position on the surface of the film when viewed in a plan view. When three or more virtual straight lines are drawn, the length of the projection is 0.1 to 5.0 μm, when the average value of the length of the plurality of line segments, which is the part that crosses the projection, is defined as the length of the projection. Worked.

And surprisingly, it has also been found that the excellent adhesion to the adhesive of the present invention and the excellent corrosion resistance are exhibited by the cross-sectional structure of the film and the morphological structure of the surface being integrated.

In addition, the inventor of the present invention conducts a conditional examination for forming the film of the present invention on a plated steel sheet, and uses a water-based surface treatment agent containing an acrylic resin to provide a manufacturing method for forming the film of the present invention on a plated steel sheet. Succeeded in establishing.

The summary of the present invention is as follows.

[1] having a steel sheet, a plating layer containing zinc formed on the steel sheet, and a film formed on the plating layer,

The film contains acrylic resin, zirconium, vanadium, phosphorus and cobalt,

In a region from the surface in the cross section of the film to a thickness of 1/5 of the film thickness, the area ratio of the acrylic resin is 80 to 100 area%,

Area ratio of the acrylic resin in a region consisting of a region from the film thickness center of the film to a thickness of 1/10 to the surface side and a region from the film thickness center to the plating layer side to a thickness of 1/10 A surface-treated steel sheet having 5 to 50% by area.

[2] On the surface of the film, there are a plurality of island-like projections in plan view,

In plan view, when three or more imaginary straight lines having a length of 10 μm or more and extending in an arbitrary direction are drawn at an arbitrary position on the surface of the film, the imaginary straight line is a portion that crosses the protrusion. The surface-treated steel sheet according to [1], wherein, when the average value of the length of the line segment is defined as the length of the protrusion, the length of the protrusion is 0.1 to 5.0 µm.

[3] The arithmetic mean roughness (Ra) of the surface of the film in a rectangular area of 1 μm on one side is 5 to 50 nm, the maximum cross-sectional height (Rt) of the roughness curve is 50 to 500 nm, and the root mean square roughness ( The surface-treated steel sheet according to [2], wherein Rq) is 10 to 100 nm.

[4] The surface treatment according to [2] or [3], wherein the concentration of zirconium in the region between adjacent projections in the coating is lower than the concentration of zirconium in the region in which the projections are formed. Grater.

[5] Any of [2] to [4], wherein the concentration of the acrylic resin in the region between the adjacent projections in the film is higher than the concentration of the acrylic resin in the region in which the projections are formed. Surface-treated steel sheet described in one.

[6] in the film, the mass ratio (V/Zr) of the mass of the vanadium and the mass of the zirconium is 0.07 to 0.69,

The mass ratio (P/Zr) of the mass of the phosphorus and the mass of the zirconium is 0.04 to 0.58,

The surface-treated steel sheet according to any one of [1] to [5], wherein a mass ratio (Co/Zr) of the mass of the cobalt and the mass of the zirconium is 0.005 to 0.08.

[7] The surface-treated steel sheet according to any one of [1] to [6], wherein the zirconium is contained in the coating film in terms of metal of 4 to 400 mg/m 2.

[8] The surface-treated steel sheet according to any one of [1] to [7], wherein the area ratio of the acrylic resin in the cross section of the film is 20 to 60 area%.

[9] In any one of [1] to [8], wherein the plating layer is composed of at least one of 60% by mass or less Al, 10% by mass or less Mg, and 2% by mass or less Si, and zinc and impurities. Surface-treated steel plate described.

[10] The acrylic resin comprises 15 to 25 mass% of styrene, 1 to 10 mass% of (meth)acrylic acid, 40 to 58 mass% of (meth)acrylate alkyl ester, and 20 to 38 mass% of acrylic. The surface-treated steel sheet according to any one of [1] to [9], which is a copolymer of ronitrile, and wherein the acrylic resin has a glass transition temperature of -12 to 24°C.

[11] The surface-treated steel sheet according to any one of [1] to [10], in which the film contains 5% by mass or less of fluoride ions.

[12] It is a manufacturing method of the surface-treated steel sheet according to any one of [1] to [11],

A step of forming a plating layer containing zinc on a steel sheet, and

Applying an aqueous surface treatment agent containing acrylic resin, zirconium, vanadium, phosphorus and cobalt on the plating layer using a roll coater, and forming a coating film;

A step of holding the coating film for at least 0.5 seconds until drying of the coating film is started after the coating film is formed;

The process of drying the coating film

A method for producing a surface-treated steel sheet having.

[13] The method for producing a surface-treated steel sheet according to [12], wherein, in the step of applying the water-based surface treatment agent, the temperature of the steel sheet when the steel sheet rushes into the roll coater is 5°C or more and 80°C or less. .

The surface-treated steel sheet of the present invention has a film having good adhesion to an adhesive and excellent corrosion resistance on its surface.

1 is a schematic diagram for explaining a cross-sectional structure of a surface-treated steel sheet according to a first embodiment.
Fig. 2 is a schematic diagram showing the surface of a film included in the surface-treated steel sheet of the first embodiment.
3 is a schematic diagram for explaining a cross-sectional structure of a surface-treated steel sheet according to a second embodiment.
4 is a TEM image of a cross section of a surface-treated steel sheet according to Example 42.
5 is a TEM image of a cross section of a surface-treated steel sheet according to Example 41.
6 is a TEM image of a cross section of a surface-treated steel sheet according to Example 3. FIG.
Fig. 7 is an image obtained by observing the surface of the surface-treated steel sheet according to Example 112 with an SEM, and a photograph showing three virtual straight lines drawn on the image.
8 is a photograph showing an image obtained by observing the surface of a surface-treated steel sheet according to Example 109 with an SEM, and three virtual straight lines drawn on the image.
9 is an SEM image of the surface of a surface-treated steel sheet according to Example 70.
10 is an AFM image of the surface of a surface-treated steel sheet according to Example 70. FIG.
11 is an SEM image of the surface of a surface-treated steel sheet according to Example 111. FIG.
12 is an AFM image of the surface of a surface-treated steel sheet according to Example 111.
13 is an SEM image of the surface of a surface-treated steel sheet according to Comparative Example 9. FIG.
14 is an AFM image of the surface of a surface-treated steel sheet according to Comparative Example 9. FIG.
15 is an SEM image of the surface of a surface-treated steel sheet according to Comparative Example 8. FIG.
16 is an AFM image of the surface of a surface-treated steel sheet according to Comparative Example 8. FIG.
17 is a TEM image of a cross section of a surface-treated steel sheet as a specific example of the surface-treated steel sheet according to the first embodiment.
18 is an SEM image of the surface of the surface-treated steel sheet shown in FIG. 17.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant descriptions are omitted.

1. Surface treatment steel plate

1.1 First embodiment

1 is a schematic diagram for explaining a cross-sectional structure of a surface-treated steel sheet according to a first embodiment.

The surface-treated steel sheet 10 shown in FIG. 1 includes a steel sheet 1, a plating layer 2 containing zinc formed on the surface 1a (the upper surface in FIG. 1) of the steel sheet 1, and a plating layer 2 It has a film 3 formed thereon.

In the surface-treated steel sheet 10 shown in FIG. 1, a case in which the plating layer 2 and the film 3 are formed only on the surface 1a side of one side of the steel sheet 1 is described as an example, but the surface of the present invention The treated steel sheet may have a plating layer and a film formed on both surfaces of the steel sheet. Further, when the plating layer 2 is formed on both surfaces of the steel sheet 1, the coating 3 may be formed only on one surface or on both surfaces.

(Steel plate)

In this embodiment, the steel plate 1 on which the plating layer 2 is formed on the surface 1a is not particularly limited. For example, as the steel plate 1, an extremely low C type (ferrite main structure), Al-k type (structure containing pearlite in ferrite), two-phase structure type (for example, a structure containing martensite in ferrite) , A steel sheet of any type, such as a structure containing bainite in ferrite), a processed organic transformation type (structure containing residual austenite in ferrite), and a fine crystal type (ferrite main structure) may be used.

(Plating layer)

The plating layer 2 is formed on one or both surfaces of the steel plate 1. The plating layer 2 should just contain zinc, and it is preferable that it consists of at least 1 type of 60 mass% or less Al, 10 mass% or less Mg, and 2 mass% or less Si, zinc and impurities. Impurities mean impurities mixed in a manufacturing process, etc., for example, Pb, Cd, Sb, Cu, Fe, Ti, Ni, B, Zr, Hf, Sc, Sn, Be, Co, Cr, Mn, Mo, P, Nb, V, Bi, and further, Group III elements such as La, Ce, and Y. It is preferable that the total of these impurity elements is about 0.5% by mass or less.

When the plating layer 2 is made of at least one of 60% by mass or less of Al, 10% by mass or less of Mg, and 2% by mass or less of Si, zinc and impurities, a surface-treated steel sheet having more excellent corrosion resistance It becomes (10).

The amount of plating deposited on the plating layer 2 is not particularly limited, and may be within a conventionally known general range.

(film)

The film 3 is formed on the plating layer 2.

The film 3 shown in FIG. 1 is composed of a particulate acrylic resin 31 and an inhibitor phase 32. The inhibitor phase 32 contains zirconium, vanadium, phosphorus and cobalt.

The ``acrylic resin'' in the present embodiment is preferably a resin containing a polymer of an alkyl (meth)acrylate, and may be a polymer obtained by polymerizing only an alkyl (meth)acrylate, or an alkyl (meth)acrylate, It may be a copolymer obtained by polymerizing other monomers. In addition, in this specification, "(meth)acryl" means "acrylic" or "methacryl."

The acrylic resin contributes to the improvement of the adhesion between the film 3 and the top coat layer and the adhesiveness with the adhesive, and contributes to the improvement of the corrosion resistance of the surface-treated steel sheet 10.

As the acrylic resin, it is preferable to use a copolymer of an alkyl (meth)acrylate and other monomers. As a copolymer, it is preferable to use a copolymer of styrene (b1), (meth)acrylic acid (b2), (meth)acrylic acid alkyl ester (b3), and acrylonitrile (b4).

In particular, as an acrylic resin, 15 to 25 mass% of styrene (b1), 1 to 10 mass% of (meth)acrylic acid (b2), 40 to 58 mass% of an alkyl (meth)acrylate (b3), It is preferable to use a copolymer of 20 to 38% by mass of acrylonitrile (b4). By using such a copolymer as an acrylic resin, the film 3 is obtained, which further has good adhesion to the top coat layer and adhesion to the adhesive, and has excellent corrosion resistance.

The component ratio of styrene (b1), (meth)acrylic acid (b2), (meth)acrylate alkyl ester (b3), and acrylonitrile (b4) in the acrylic resin is determined by infrared absorption (IR) analysis, Raman analysis, mass analysis, etc. It can be calculated by analyzing the film using an analysis method.

Styrene (b1) increases the adhesion between the plating layer 2 of the coating film 3 and the top coat layer, and improves the corrosion resistance of the surface-treated steel sheet 10. When 15% by mass or more of styrene (b1) is contained with respect to the total mass of the monomer component, the effect obtained by styrene (b1) is further improved. The content of styrene (b1) is more preferably 17% by mass or more. When the content of styrene (b1) is 25% by mass or less, the content of styrene (b1) is too large to prevent the film 3 from becoming hard. As a result, the adhesion between the film 3 and the plating layer 2 and the top coat layer is further improved, and the corrosion resistance of the surface-treated steel sheet 10 is further improved. The content of styrene (b1) is more preferably 23% by mass or less.

The (meth)acrylic acid (b2) improves the adhesion between the film 3, the plating layer 2, and the top coat layer, and increases the corrosion resistance of the surface-treated steel sheet 10. When 1 mass% or more of (meth)acrylic acid (b2) is contained with respect to the total mass of a monomer component, the effect obtained by (meth)acrylic acid (b2) is further improved. The content of (meth)acrylic acid (b2) is more preferably 2% by mass or more. When the content of (meth)acrylic acid (b2) is 10% by mass or less, the water resistance of the film 3 becomes good, and more excellent corrosion resistance is obtained. It is more preferable that the content of (meth)acrylic acid (b2) is 6% by mass or less.

The (meth)acrylate alkyl ester (b3) improves the corrosion resistance of the surface-treated steel sheet 10. When 40 mass% or more of (meth)acrylate alkyl ester (b3) is contained with respect to the total mass of a monomer component, more excellent corrosion resistance is obtained. When the content of the alkyl (meth)acrylate (b3) is 58% by mass or less, more excellent corrosion resistance is obtained. The content of the alkyl (meth)acrylate (b3) is more preferably 55% by mass or less.

As the (meth)acrylate alkyl ester (b3), for example, at least one selected from methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-methylhexyl acrylate, and isomers thereof can be used. I can. Among these, it is preferable to use ethyl acrylate and/or butyl acrylate from the viewpoint of particularly excellent corrosion resistance.

Acrylonitrile (b4) improves the adhesion between the film 3 and the adhesive. When 20% by mass or more of acrylonitrile (b4) is contained with respect to the total mass of the monomer component, the adhesion between the film 3 and the adhesive is further improved. When the content of the acrylonitrile (b4) is 38% by mass or less, the water resistance of the film 3 becomes good, and more excellent corrosion resistance is obtained. It is more preferable that the content of acrylonitrile (b4) is 35% by mass or less.

When the acrylic resin is a copolymer, it may be a copolymer of styrene (b1), (meth)acrylic acid (b2), (meth)acrylic acid alkyl ester (b3), acrylonitrile (b4), and other vinyl group-containing monomers. do.

Although it does not specifically limit as another vinyl group-containing monomer, For example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2 -Hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, ethoxy-diethylene glycol (meth)acrylate, 2-hydroxyethyl (meth) allyl ether, 3-hydroxypropyl ( Meth) allyl ether, 4-hydroxybutyl (meth) allyl ether, 2-dimethylaminoethyl acrylic acid, acrylamide, allyl alcohol, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, citraconic acid, cinnamic acid , Vinyl trimethoxysilane, vinyl triethoxysilane, allyl glycidyl ether, glycidyl (meth) acrylate, 2-(1-aziridinyl) ethyl acrylate, iminol methacrylate, acryloyl Morpholine, vinyl formate, vinyl acetate, vinyl butyrate, vinyl acrylate, vinyl toluene, nitrile cinnamate, (meth)acryloxyethylphosphate, and bis-(meth)acryloxyethylphosphate, and one or more of these You can use Among these, 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, ethoxy-diethylene glycol acrylate, and acrylamide are preferred from the viewpoint of excellent emulsion stability.

In this specification, "(meth)acrylate" means "acrylate" or "methacrylate". “(Meth)allyl ether” means “allyl ether” or “metalyl ether”. "(Meth)acrylo" means "acrylo" or "methacrylo".

As for the acrylic resin, it is preferable that the glass transition temperature is -12 to 24 degreeC, and it is more preferable that it is -10 to 20 degreeC. When the glass transition temperature is -12°C or higher, the film 3 having even more excellent corrosion resistance is obtained. When the glass transition temperature is 24°C or less, the adhesion to the top coat layer and the adhesion to the adhesive are further improved.

The glass transition temperature of the acrylic resin is calculated by the following formula (1).

(In formula (1), Tg is the glass transition temperature (K) of the acrylic resin (A), W ₁ , W ₂ , ..., W _n is the weight of the homopolymer of each monomer constituting the acrylic resin Fraction, Tg ₁ , Tg ₂ , ..., Tg _n is the glass transition temperature of the homopolymer of each monomer)

It is preferable that the concentration of the acrylic resin in the entire film 3 is 20 to 60% by mass. When the concentration of the acrylic resin is 20% by mass or more, the effect of including the acrylic resin is sufficiently obtained. When the concentration of the acrylic resin is 60% by mass or less, the zirconium content can be sufficiently secured, and further excellent corrosion resistance can be obtained due to the synergistic effect of including zirconium and the acrylic resin. It is more preferable that the concentration of the acrylic resin is 40% by mass or less. Further, when the concentration of the acrylic resin in the entire film 3 is within the above range, the range of the area ratio of the acrylic resin in the "upper region A" and "center region C" described later can be achieved more reliably.

Zirconium, vanadium, phosphorus, and cobalt in the film 3 all function as corrosion inhibitors (inhibitors) of the surface-treated steel sheet 10 to improve the corrosion resistance of the surface-treated steel sheet 10. Zirconium, vanadium, phosphorus, and cobalt each have different corrosive environments in which the function as a corrosion inhibitor is effectively exhibited. For this reason, by containing four types of zirconium, vanadium, phosphorus and cobalt as corrosion inhibitors, corrosion in various corrosive environments can be suppressed, and more excellent corrosion resistance can be obtained.

The zirconium in the film 3 forms a crosslinked structure with an acrylic resin. For this reason, the film 3 has excellent barrier properties. In addition, it is estimated that zirconium in the film 3 forms a Zr-O-M bond (M: a metal element in the plating layer) with the surface of the plating layer 2. Thereby, the film 3 has excellent adhesion with the plating layer 2.

The zirconium content of the coating 3 is preferably 4 to 400 mg/m 2 in terms of metal. When the zirconium adhesion amount is 4 mg/m 2 or more, the effect of improving the adhesion due to bonding of the surface of the zirconium and the plating layer 2 and the effect of improving the barrier property due to the crosslinked structure of zirconium and the acrylic resin are further improved. As a result, even more excellent corrosion resistance is obtained. It is more preferable that the zirconium adhesion amount is 50 mg/m 2 or more. When the zirconium adhesion amount is 400 mg/m 2 or less, it is possible to prevent the occurrence of cracks due to containing zirconium in the film 3, and more excellent corrosion resistance can be obtained. It is more preferable that the zirconium adhesion amount is 350 mg/m 2 or less.

Vanadium in the film 3 is preferentially eluted to the plating layer 2 in a corrosive environment, suppresses an increase in pH due to dissolution of the plating layer 2, and improves the corrosion resistance of the surface-treated steel sheet 10.

Phosphorus in the film 3 forms a passivation film made of a poorly soluble metal salt such as zinc phosphate on the surface of the plating layer 2 to improve the corrosion resistance of the surface-treated steel sheet 10. The poorly soluble metal salt is generated by a reaction of phosphorus and metal ions generated by dissolving a part of the plating layer 2. The poorly soluble metal salt is obtained by applying a water-based treatment agent containing phosphorus used for formation of the film 3 to the plating layer 2, and/or the plating layer 2 under a corrosive environment after the formation of the film 3 As a result, a part of the plating layer 2 is dissolved and formed.

The cobalt in the film 3 improves the blackening resistance and corrosion resistance of the surface-treated steel sheet 10.

In this embodiment, when the plating layer 2 is made of a zinc-aluminum-magnesium alloy, aluminum and magnesium in the plating layer 2 exhibit a sacrificial anticorrosive effect in a corrosive environment. For this reason, a blackening phenomenon in which zinc in the plating layer 2 is oxidized in an oxygen deficient state may occur. The blackening phenomenon is likely to occur in a portion where the plating layer 2 is easily dissolved. It is estimated that cobalt in the film 3 reduces the oxidation (corrosion) rate of zinc in the plating layer 2 and prevents blackening.

The film 3 preferably has a mass ratio (V/Zr) of the mass of vanadium and the mass of zirconium of 0.07 to 0.69. When the above-described mass ratio (V/Zr) is 0.07 or more, an effect of improving corrosion resistance by vanadium is sufficiently obtained, and further excellent corrosion resistance is obtained. Further, if the above-described mass ratio (V/Zr) is 0.69 or less, since zirconium content can be secured, it is preferable. The mass ratio (V/Zr) is more preferably 0.14 to 0.56.

It is preferable that the mass ratio (P/Zr) of the mass of phosphorus to the mass of zirconium of the film 3 is 0.04 to 0.58. When (P/Zr) is 0.04 or more, an effect of improving corrosion resistance due to phosphorus is sufficiently obtained, and further excellent corrosion resistance is obtained. When the above-described mass ratio (P/Zr) is 0.58 or less, since the zirconium content can be ensured, it is preferable. The mass ratio (P/Zr) is more preferably 0.07 to 0.29.

It is preferable that the mass ratio (Co/Zr) of the mass of cobalt and the mass of zirconium of the film 3 is 0.005 to 0.08. When the above-described mass ratio (Co/Zr) is 0.005 or more, the effect of improving blackening resistance and corrosion resistance by cobalt is sufficiently obtained, further excellent corrosion resistance can be obtained, and blackening can be suppressed. If the above-described mass ratio (Co/Zr) is 0.08 or less, since zirconium content can be ensured, it is preferable. The mass ratio (Co/Zr) is more preferably 0.009 to 0.03.

The content of V, P, Co, and Zr in the film 3 can be calculated by subjecting the film 3 to fluorescence X-ray analysis and considering that V, P, Co, and Zr in the film exist as oxides. As a result of investigation by the present inventors, each component of V, P (in terms of phosphoric acid), Co, and Zr in the film calculated by the above method is the mass ratio (V, phosphoric acid, Co, Zr) to the total solid content of the aqueous surface treatment agent. ) And the correspondence. Therefore, the content (mass%) of V, P (in terms of phosphoric acid), Co, and Zr in the film can be regarded as representing the mass ratio with respect to the total solid content of the aqueous surface treatment agent as a percentage.

The film 3 may contain 5% by mass or less of fluoride ions. The fluoride ions in the film 3 are derived from a component containing fluoride ions contained as necessary in the aqueous surface treatment agent used when forming the film 3. The component containing fluoride ions is used to improve the adhesion and adhesion of the film 3. When the content of fluoride ions in the film 3 is 5% by mass or less, occurrence of condensation whitening due to containing fluoride ions can be prevented. More specifically, when the content of fluoride ions is 5% by mass or less, the amount of fluoride ions eluted in the condensation water is very small. For this reason, even if fluoride ions are concentrated and precipitated on the film 3 during the drying process of the condensed water, they are limited to trace amounts that do not appear as condensation whitening. Therefore, deterioration of the appearance (white rust generation) due to condensation whitening can be prevented. It is preferable that the content of fluoride ions in the film 3 is 3% by mass or less.

In the film 3 shown in Fig. 1, a region A from the surface 33 in the cross section of the film 3 to a thickness of 1/5 of the film thickness (hereinafter sometimes referred to as "upper region") and In the region B from the interface 34 with the plating layer 2 to a thickness of 1/5 of the film thickness (hereinafter, sometimes referred to as “lower region”), the area ratio of the acrylic resin is 80 to 100 area%. . In addition, the region C1 from the center of the film thickness of the film 3 in the cross-section of the film 3 to the thickness of 1/10 of the film thickness toward the surface 33 side (hereinafter, referred to as “upper center region”) And, a region consisting of a region C2 (hereinafter, referred to as a ``lower center region'' in some cases) from the center of the film thickness to the plating layer 2 side with a thickness of 1/10 (hereinafter, a region consisting of the region C1 and the region C2) C is sometimes referred to as a "center region"), the area ratio of the acrylic resin is 5 to 50 area%.

Therefore, in the film 3 shown in FIG. 1, the concentration of the acrylic resin 31 in the upper region A and the lower region B is higher than the concentration of the acrylic resin 31 in the center region C.

In the film 3 shown in Fig. 1, since the area ratio of the acrylic resin 31 in the upper region A in the cross section of the film 3 is 80 area% or more, a high concentration acrylic resin present on the surface 33 By (31), elution of corrosion inhibitors (zirconium, vanadium, phosphorus, cobalt) from the film 3 in a humid environment is suppressed. For this reason, the barrier property by the film 3 is exhibited over a long period of time, and excellent corrosion resistance is obtained. In addition, since the area ratio of the acrylic resin 31 in the upper region A is 80 area% or more, good adhesion between the film 3 and the adhesive is obtained by the acrylic resin 31 having a high concentration present on the surface 33. Lose. The area ratio of the acrylic resin 31 in the upper region A in the cross section of the film 3 is preferably 90 area% or more, and may be 100 area%. In addition, it is preferable that the area ratio of the acrylic resin 31 in the upper region A in the cross section of the film 3 is high toward the surface 33 from the center of the film thickness. In this case, the effect of the presence of the acrylic resin 31 in the upper region A becomes even more remarkable.

In addition, in this embodiment, since the area ratio of the acrylic resin 31 in the lower region B in the cross section of the film 3 is 80 area% or more, the interface 34 with the plating layer 2 of the film 3 Eh, the acrylic resin 31 is present in a high concentration. For this reason, in the interface 34 between the film 3 and the plating layer 2, good adhesion is obtained. As a result, in the surface-treated steel sheet 10 of the present embodiment, instead of the film 3, compared to the case where, for example, a film having the same amount of acrylic resin in the film and a uniform acrylic resin concentration throughout the film is formed, Excellent corrosion resistance is obtained. In order to improve the adhesion at the interface 34, the area ratio of the acrylic resin 31 in the lower region B in the cross section of the film 3 is preferably 90 area% or more, and may be 100 area%.

Since the area ratio of the acrylic resin 31 in the central region C in the cross section of the film 3 is 5 area% or more, the effect of improving the barrier property by the crosslinked structure of zirconium and the acrylic resin is obtained. It is preferable that the area ratio of the acrylic resin 31 in the center region C is 10 area% or more.

Since the area ratio of the acrylic resin 31 in the central region C in the cross section of the film 3 is 50 area% or less, the inhibitor phase 32 (zirconium, vanadium, phosphorus, cobalt) is sufficiently contained in the film 3 It contains, and excellent corrosion resistance and blackening resistance are obtained. It is preferable that the area ratio of the acrylic resin 31 in the center region C is 40 area% or less.

It is preferable that the area ratio of the acrylic resin 31 in the entire cross section of the film 3 is 20 to 60 area%. When the area ratio of the acrylic resin 31 in the cross section of the film 3 is 20 area% or more, the effect of including the acrylic resin 31 is sufficiently obtained. It is more preferable that the area ratio of the acrylic resin 31 is 30 area% or more. If the area ratio of the acrylic resin 31 in the entire cross section of the film 3 is 60 area% or less, the area ratio of the inhibitor phase 32 (zirconium, vanadium, phosphorus, cobalt) can be sufficiently secured, Further excellent corrosion resistance is obtained by synergistic effect by including the inhibitor phase 32 and the acrylic resin 31. It is more preferable that the area ratio of the acrylic resin 31 is 50 area% or less.

In addition, the film 3 of the surface-treated steel sheet 10 according to the present embodiment has a surface structure as shown in FIG. 2. Fig. 2 is a schematic diagram showing the surface of a film of the surface-treated steel sheet according to the present embodiment. On the surface of the film 3 shown in FIG. 2, a plurality of protrusions 35 are densely present. The protrusion 35 is a protrusion-shaped part (island part) confirmed by observing the surface of the surface-treated steel sheet using an atomic force microscope (AFM). Each protrusion 35 has an irregular, uneven island shape in plan view. It is preferable that the length of the protrusion 35 is 0.1 to 5.0 μm. In addition, a region between the adjacent projections 35 and 35 is a recessed valley, and the entire periphery of each projection 35 is surrounded by the valley. In addition, the shape of each protrusion 35 is not limited to the illustrated embodiment, and may be substantially the same, and may have a certain shape, such as a square, a hexagon, a substantially circular, and an approximately ellipse.

The length of the protrusion 35 in this embodiment is a value calculated by the method shown below. First, as shown in Fig. 2, at an arbitrary position on the surface of the film 3, three or more imaginary straight lines L having a length of 10 μm or more and extending in an arbitrary direction (in Fig. 2, one imaginary straight line Only, but the same applies to other virtual straight lines). Next, with respect to all the protrusions 35 and 35 crossed by three or more imaginary straight lines L, the length of a plurality of line segments of the portion in which three or more imaginary straight lines L cross the plurality of protrusions 35 and 35 (for example, , Symbols a, b, c, d) in FIG. 2 are measured. Then, the average value (for example, the average value of a, b, c, d, ...) of the lengths of the plurality of line segments of the portion where the virtual straight line L crosses the projections 35, 35 is calculated, and the average value is calculated. It should be the length of (35).

In addition, when measuring the length of the protrusion 35, an image obtained by observing the surface of the film 3 with a scanning electron microscope (SEM) can be used. When the length of the projections 35 is measured using the SEM image, the outline of each projection 35 can be identified by the intensity of the contrast (contrast difference).

In particular, when the length of the protrusion 35 is 5.0 µm or less, cracks caused by the coating 3 containing zirconium can be prevented from occurring in the coating 3, and further excellent corrosion resistance can be obtained. The length of the protrusion 35 is more preferably 2.0 μm or less in order to more effectively prevent cracking of the film 3. On the other hand, if the length of the protrusion 35 is excessively short, the wettability of the paint used to form the top coat layer on the film 3 decreases, and the anchoring effect of the protrusion 35 with respect to the top coat layer may decrease. have. In particular, when the length of the protrusion 35 is 0.1 μm or more, the anchoring effect of the protrusion 35 to the top coat layer or adhesive formed on the film 3 is sufficiently obtained. As a result, the adhesion between the film 3 and the adhesive is further improved, the adhesion to the top coat layer is improved, and a surface-treated steel sheet having excellent corrosion resistance is obtained. The length of the protrusion 35 is more preferably 0.2 µm or more in order to increase the anchoring effect of the protrusion 35.

The minimum value among the lengths of all the projections 35 measured to calculate the length of the projections 35 (minimum value of the lengths of the virtual straight line crossing the projection image in all projections crossed by the above three or more virtual straight lines) Silver is preferably 0.1 µm or more, and more preferably 0.2 µm or more. When the minimum value of the length of the protrusion 35 is 0.1 µm or more, the anchoring effect of the protrusion 35 to the top coat layer or adhesive formed on the film 3 becomes remarkable.

In addition, the maximum value among the lengths of the protrusions 35 measured to calculate the length of the protrusions 35 (the maximum value among the lengths of the virtual straight lines crossing the protrusions in all protrusions crossed by the three or more virtual straight lines described above ) Is preferably 5.0 µm or less, and more preferably 2.0 µm or less. When the maximum value of the length of the protrusion 35 is 5.0 µm or less, the crack of the film 3 can be more effectively prevented.

The arithmetic mean roughness (Ra) of the surface of the film 3 in a rectangular area of 1 μm on one side is 5 to 50 nm, the maximum cross-sectional height (Rt) of the roughness curve is 50 to 500 nm, and the root mean square roughness (Rq) Is preferably 10 to 100 nm. When Ra, Rt, and Rq on the surface of the film 3 are within the above range, since Ra, Rt, and Rq are sufficiently large, the surface of the film 3 (the surface of the projection 35) is appropriately rough. Due to the anchor effect, the adhesion between the film 3 and the top coat layer and the adhesion to the adhesive are further improved. In order to further improve the above anchor effect, it is more preferable that the arithmetic mean roughness (Ra) is 10 nm or more, the maximum cross-sectional height (Rt) of the roughness curve is 100 nm or more, and the root mean square roughness (Rq) is 20 nm or more. Do.

When Ra, Rt, and Rq on the surface of the film 3 are within the above range, since Ra, Rt, and Rq are sufficiently small, cracks caused by the film 3 containing zirconium can be more effectively prevented. There is, and more excellent corrosion resistance is obtained. In order to further improve the above-described crack prevention effect, it is more preferable that the arithmetic mean roughness (Ra) is 40 nm or less, the maximum cross-sectional height (Rt) of the roughness curve is 400 nm or less, and the root mean square roughness (Rq) is 80 nm or less. Do.

The concentration of zirconium in the region (valley) between the adjacent projections 35 and 35 in the coating 3 is lower than the concentration of zirconium in the region (island region) where the projections 35 are formed. desirable. In this case, further excellent corrosion resistance is obtained by the barrier property of the coating 3 containing zirconium.

The concentration of zirconium in the "area between adjacent projections 35" and "area in which the projections 35 are formed" in the film 3 is EPMA (electron beam microanalyzer) or SEM/EDX (Note It can be confirmed by a method of analyzing the coating film 3 from the surface using a tetragonal electron microscope/energy dispersive X-ray spectroscopy).

In addition, the concentration of the acrylic resin in the region (valley) between the adjacent projections 35 and 35 in the coating 3 is the acrylic resin in the region (island region) where the projections 35 are formed. It is preferably higher than the concentration. In this case, with the acrylic resin aggregated between the adjacent projections 35, better adhesion between the film 3 and the top coat layer is obtained, and better adhesion between the film 3 and the adhesive. Is obtained.

It can be confirmed by the method shown below that the acrylic resin is agglomerated between the adjacent projections 35 and 35. That is, the surface of the film 3 is analyzed using EPMA (electron beam microanalyzer) or SEM/EDX (scanning electron microscope/energy dispersive X-ray spectroscopy).

In the film of the present embodiment, since the carbon component detected by the above analysis method is derived from an acrylic resin, the distribution of the carbon component detected by the above analysis method is regarded as the distribution of the acrylic resin and evaluated.

In addition, that the carbon component in the film is derived from an acrylic resin can be confirmed by the method shown below. That is, the film peeled off from the surface-treated steel sheet by acid treatment is subjected to infrared spectroscopy analysis and pyrolysis GC-MS (gas chromatograph-mass spectrometry) analysis. From the result of analysis from the attribution of the observed absorption derived from the resin component in the infrared absorption spectrum of the film obtained by infrared spectral analysis and the analysis result of pyrolysis GC-MS, it can be confirmed that the carbon component in the film is derived from acrylic resin. have.

Since the surface-treated steel sheet 10 according to the present embodiment has a film 3 in which a plurality of island-like projections 35 and 35 are present on the surface in a plan view of a specific size, the adhesion to the adhesive is further improved. It is better and the adhesion with the top coat layer is good.

In addition, in the surface-treated steel sheet 10 according to the present embodiment, the zirconium contained in the film 3 and the acrylic resin 31 form a crosslinked structure. Further, zirconium in the film 3 forms a Zr-O-M bond (M: a metal element in the plating layer) with the surface of the plating layer 2. Due to these points, the film 3 of the surface-treated steel sheet 10 has excellent adhesion to the plating layer 2 and has excellent barrier properties. Therefore, the surface-treated steel sheet 10 has excellent corrosion resistance.

Next, with reference to Figs. 4, 17, and 18, the correlation between the cross-sectional structure and the surface structure of the surface-treated steel sheet 10 according to the present embodiment will be described. In FIG. 17, a TEM image of a cross section of a steel sheet as a specific example (Example 42 to be described later) of the surface-treated steel sheet 10 according to the present embodiment is shown in FIG. 18, and in FIG. 18, an SEM image of the surface of the surface-treated steel sheet according to FIG. Represents. As shown in FIGS. 4 and 17, in the cross section of the surface-treated steel sheet 10 according to the present embodiment, in the range of the upper region A including the center region C of the film 3 to the lower region B, the acrylic resin is A point connected in the thickness direction is observed. As shown in FIG. 18, the point is a point where acrylic resin is aggregated between the adjacent projections 35, 35 in surface observation, and the valley portion between the projection 35 and the projection 35 It corresponds to (refer to the points indicated by a plurality of arrows in Fig. 18). That is, when the acrylic resin extends in a column shape in the thickness direction from the cross-section of the film 3, an aggregation point of the acrylic resin is formed. When only the inhibitor phase (zirconium, vanadium, phosphorus, cobalt) is present in the film and no acrylic resin is present, a crack occurs as shown in Fig. 13 (Comparative Example 9 of Example) described later, but in this embodiment, acrylic resin The columnar bridge portions made of are formed at intervals of micrometer order, thereby acting as a buffering material, and cracking of the film 3 is suppressed.

That is, the film 3 of the surface-treated steel sheet 10 according to the present embodiment has a barrier effect (long-term corrosion resistance) of preventing the elution of the corrosion inhibitor by (1) agglomeration of acrylic resin on the surface of the film 3, (2) In the film (3), acrylic resin is agglomerated like a column to support the portion between the protrusions 35 and the valleys of the protrusions 35 on the surface (inhibition of cracking, adhesion with adhesive, top coat) It has a remarkable structure that exhibits adhesion to the layer).

The mechanism for forming the cross-section and the structure of the surface of the film 3 of the surface-treated steel sheet 10 according to the present embodiment is the steel sheet rush temperature in the application step of the water-based surface treatment agent containing acrylic resin, and the time from application to drying. It is presumed to be related to the back. For that reason, when the steel plate 1 and the aqueous surface treatment agent containing acrylic resin come into contact, the surface free energy difference between the acrylic resin and other components in the coating film on the surface 1a of the steel plate 1 causes acrylic This is because it is assumed that a special structure is formed by the surface adsorption and interface adsorption of the resin. In addition, as important factors that determine the moving speed and moving time of the acrylic resin in the coating film, the steel sheet rush temperature, the time from application to drying, and the like can be cited.

1.2 Second embodiment

3 is a schematic diagram for explaining a cross-sectional structure of a surface-treated steel sheet according to a second embodiment.

The surface-treated steel plate 20 shown in FIG. 3 is formed on the steel plate 1 and the surface 1a of the steel plate 1 (the upper surface in FIG. 3), similarly to the surface-treated steel plate 10 shown in FIG. It has a plating layer 2 containing zinc, and a film 3a formed on the plating layer 2.

In the surface-treated steel sheet 20 shown in FIG. 3, the surface-treated steel sheet 10 shown in FIG. 1 and the concentration distribution of the acrylic resin 31 in the film are different. Specifically, in the surface-treated steel sheet 20 shown in Fig. 3, the region B (the lower part) from the interface 34 with the plating layer 2 in the cross section of the film 3a to a thickness of 1/5 of the film thickness. The area ratio of the acrylic resin in the area) is less than 80 area%. Therefore, in the surface-treated steel sheet 20, since the area ratio of the inhibitor phase 32 (zirconium, vanadium, phosphorus, cobalt) in the region B is sufficiently secured, the effect of improving the corrosion resistance by the inhibitor phase 32 is obtained. It is obtained effectively.

The surface-treated steel sheet 20 of the present embodiment has an area ratio of the acrylic resin 31 in the upper region A in the cross section of the film 3a, similar to the surface-treated steel sheet 10 shown in FIG. Since it is not less than %, elution of corrosion inhibitors (zirconium, vanadium, phosphorus, cobalt) from the film 3a in a wet environment is suppressed by the acrylic resin 31 having a high concentration present on the surface 33. For this reason, the barrier property by the film 3a is exhibited over a long period of time, and excellent corrosion resistance is obtained. In addition, since the area ratio of the acrylic resin 31 in the upper region A is 80 area% or more, good adhesion between the film 3a and the adhesive is obtained by the acrylic resin 31 having a high concentration present on the surface 33. Lose.

In addition, in the surface-treated steel sheet 20 according to the present embodiment, since the area ratio of the acrylic resin 31 in the central region C in the cross section of the film 3a is 5 area% or more, the crosslinked structure of zirconium and acrylic resin The barrier property improvement effect is obtained. In addition, since the area ratio of the acrylic resin 31 in the central region C in the cross section of the film 3a is 50 area% or less, the inhibitor phase 32 (zirconium, vanadium, phosphorus, cobalt) in the film 3a It sufficiently contains, and excellent corrosion resistance and blackening resistance are obtained.

In addition, the surface-treated steel sheet 20 also has a surface structure as shown in FIG. 2 similarly to the surface-treated steel sheet 10. Therefore, the surface-treated steel sheet 20 has good adhesiveness with an adhesive and good adhesiveness with a top coat layer.

In addition, in the surface-treated steel sheet 20, similarly to the surface-treated steel sheet 10 shown in FIG. 1, the zirconium and acrylic resin 31 contained in the film 3a form a crosslinked structure. Further, zirconium in the film 3a forms a Zr-O-M bond (M: a metal element in the plating layer) with the surface of the plating layer 2. Due to these points, the film 3a of the surface-treated steel sheet 20 has excellent adhesion to the plating layer 2 and has excellent barrier properties. Therefore, the surface-treated steel sheet 20 has more excellent corrosion resistance.

Next, with reference to FIG. 5, the correlation between the cross-sectional structure and the surface structure of the surface-treated steel sheet 20 according to the second embodiment will be described. In the second embodiment as well as in the first embodiment, in the cross section of the film 3a of the surface-treated steel sheet 20, in the range of the upper region A including the center region C of the film 3a to the lower region B, acrylic A point where the resin leads in the thickness direction is observed. The said location is a location where acrylic resin aggregates in the valley part between adjacent projections 35, 35 in the above-mentioned surface observation. That is, when the said acrylic resin extends in the thickness direction from the cross section of the film 3a, the aggregation point of the acrylic resin is formed. Thereby, as described in the above-described first embodiment, cracks in the surface layer of the film 3a are suppressed, and the adhesiveness to the adhesive and the adhesion to the top coat layer are improved (bridge effect). The second embodiment has the same structure as the first embodiment.

2. Manufacturing method of surface-treated steel sheet

Next, a method of manufacturing the surface-treated steel sheets 10 and 20 according to the first and second embodiments described above will be described by way of example.

First, a steel plate 1 is prepared, and a plated layer 2 containing zinc is formed on one or both surfaces of the steel plate 1 by a known method.

Next, a water-based surface treatment agent containing each component contained in the films 3 and 3a of the first and second embodiments in a predetermined ratio is applied on the plating layer 2 and dried, thereby drying the plating layer ( 2) Films 3 and 3a are formed on it.

(Aqueous surface treatment agent)

The aqueous surface treatment agent contains acrylic resin, zirconium, vanadium, phosphorus and cobalt. In this embodiment, as an aqueous surface treatment agent, for example, a zirconium carbonate compound (A), an acrylic resin (B), a vanadium compound (C), a phosphorus compound (D), a cobalt compound (E), and water are mixed. A pH of 8 to 11 is used.

(Acrylic resin (B))

The acrylic resin (B) becomes the acrylic resin 31 contained in the above-described films 3 and 3a by applying and drying an aqueous surface treatment agent.

It is preferable that the content of the acrylic resin (B) in the aqueous surface treatment agent is 20 to 60 mass% with respect to the total solid content of the aqueous surface treatment agent. The content of the acrylic resin (B) in the aqueous surface treatment agent is more preferably 20 to 40% by mass. When the content of the acrylic resin (B) in the aqueous surface treatment agent is 20% by mass or more, the coatings 3 and 3a having a concentration of 20 to 60% by mass of the acrylic resin 31 in the entire coatings 3 and 3a can be formed. Because it can be, it is preferable.

The polymerization method of the acrylic resin (B) used for the aqueous surface treatment agent is not particularly limited. For example, suspension polymerization, emulsion polymerization and solution polymerization can be used. Further, when polymerizing the acrylic resin (B), a solvent and/or a polymerization initiator may be used. Although it does not specifically limit as a polymerization initiator, For example, radical polymerization initiators, such as an azo-type compound and a peroxide-type compound, can be used. It is preferable to use 0.1-10 mass% of a polymerization initiator with respect to the total solid content of resin. The reaction temperature is usually room temperature to 200°C, preferably 40 to 150°C. The reaction time is 30 minutes to 8 hours, preferably 2 to 4 hours.

(Zirconium carbonate compound (A))

The zirconium carbonate compound (A) in the water-based surface treatment agent is crosslinked with the acrylic resin (B) by applying and drying the water-based surface treatment agent, and coatings (3, 3a) having a crosslinked structure of zirconium and the acrylic resin 31 ) To form. In addition, when the zirconium carbonate compound (A) is applied and dried with an aqueous surface treatment agent, carbonate ions are volatilized, and the remaining zirconiums are bonded to each other through oxygen, resulting in a high molecular weight. In this process, -Zr-OH groups form a Zr-O-M bond (M: a metal element in the plating layer) with the surface of the plating layer 2.

The type of the zirconium carbonate compound (A) is not particularly limited, and examples thereof include zirconium carbonate, ammonium zirconium carbonate, potassium zirconium carbonate, sodium zirconium carbonate, and the like, and one or more of these can be used. Among these, it is preferable to use zirconium carbonate and/or ammonium zirconium carbonate because the coatings 3 and 3a excellent in corrosion resistance are obtained.

(Vanadium compound (C))

As the vanadium compound (C) contained in the aqueous surface treatment agent, for example, vanadium pentoxide (V ₂ O ₅ ), metavanadic acid (HVO ₃ ), ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride (VOCl ₃₎ ), etc., reduced to 2 to 4 by a reducing agent, vanadium trioxide (V ₂ O ₃ ), vanadium dioxide (VO ₂ ), vanadium oxysulfate (VOSO ₄ ), vanadium oxyoxalate [VO (COO ) ₂ ], (vanadium oxyacetylacetonate [VO(OC(CH ₃ )=CHCOCH ₃ )) ₂ ], vanadium acetylacetonate[V(OC(CH ₃ )=CHCOCH ₃ )) ₃ ], vanadium trichloride (VCl ₃ ), invanad molybdic acid {H _15-X [PV _12-x Mo _x O ₄₀ ]·nH ₂ O (6<x<12, n<30)}, vanadium sulfate (VSO ₄ ·8H ₂ O), And vanadium compounds having 4 to divalent oxidation numbers such as vanadium dichloride (VCl ₂ ) and vanadium oxide (VO).

(Phosphorus compound (D))

Examples of the phosphorus compound (D) contained in the aqueous surface treatment agent include an inorganic acid anion having an acid group containing phosphorus, an organic acid anion having an acid group containing phosphorus, and the like.

As the inorganic acid anion having an acid group containing phosphorus, for example, inorganic acid anions in which at least one hydrogen is free from inorganic acids such as orthophosphoric acid, metaphosphoric acid, condensed phosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, tetraphosphoric acid, hexametaphosphoric acid, and their Salts are mentioned.

As an organic acid anion having an acid group containing phosphorus, for example, 1-hydroxymethane-1,1-diphosphonic acid, 1-hydroxyethane-1,1-diphosphonic acid, 1-hydroxypropane-1, 1-diphosphonic acid, 1-hydroxyethylene-1,1-diphosphonic acid, 2-hydroxyphosphonoacetic acid, aminotri(methylenephosphonic acid), ethylenediamine-N,N,N',N'-tetra (Methylenephosphonic acid), hexamethylenediamine-N,N,N',N'-tetra(methylenephosphonic acid), diethylenetriamine-N,N,N',N'',N''-penta(methylene Phosphonic acid), 2-phosphonic acid butane-1,2,4-tricarboxylic acid, inositol hexaphosphonic acid, organic phosphonic acids such as phytic acid, organic acid anions in which at least one hydrogen is released, such as organic phosphoric acid, and salts thereof Can be mentioned.

(Cobalt compound (E))

Examples of the cobalt compound (E) contained in the aqueous surface treatment agent include cobalt sulfate, cobalt nitrate, and cobalt carbonate.

(slush)

The aqueous surface treatment agent may contain a lubricant in order to improve the scratch resistance of the surface-treated steel sheet. Examples of the lubricant include polyethylene wax, oxidized polyethylene wax, and oxidized polypropylene wax.

The content of the lubricant is preferably 1 to 8% by mass based on the total solid content of the aqueous surface treatment agent. When the content of the lubricant is 1% by mass or more, the effect of improving the scratch resistance is sufficiently obtained. In addition, when the content of the lubricant is 8% by mass or less, it is possible to prevent the coating adhesion of the film 3 from deteriorating by including the lubricant.

It is preferable that the lubricant has a mass average particle diameter of 0.1 to 5.0 µm. When the mass average particle diameter is 0.1 µm or more, the lubricant is less likely to aggregate, resulting in an aqueous surface treatment agent having excellent stability. Moreover, when the mass average particle diameter of a lubricant is 5.0 micrometers or less, dispersion stability becomes favorable.

The method for measuring the mass average particle diameter of the lubricant is not limited, but can be measured, for example, by Nikisso Corporation (laser diffraction scattering particle size distribution measuring apparatus MICROTRAC HRA-X100).

(pH)

The pH of the aqueous surface treatment agent is preferably 8 to 11, more preferably 8.5 to 10. When the pH of the aqueous surface treatment agent is 8 or more, the zirconium carbonate compound (A) can be stably dissolved in the aqueous surface treatment agent. On the other hand, when the pH of the aqueous surface treatment agent is 11 or less, when the aqueous surface treatment agent is applied to the plating layer 2, excessive dissolution of the plating layer 2 can be suppressed. In addition, when the pH is within the range, the aqueous surface treatment agent is stabilized.

The method of measuring the pH of the water-based surface treatment material is not limited, for example, it can be measured at a measurement temperature of 25°C using the Toa DKK Co., Ltd. product (HM-30R).

The adjusting agent used for adjusting the pH of the aqueous surface treatment material is not particularly limited, and examples thereof include ammonia, guanidine carbonate, carbonic acid, acetic acid, and hydrofluoric acid.

(Component containing fluoride ion)

The aqueous surface treatment agent may contain a component containing a fluoride ion, if necessary. The component containing fluoride ions is used to improve the adhesion and adhesion of the films 3 and 3a.

As a component containing fluoride ions contained in the aqueous surface treatment agent, for example, ammonium zirconium fluoride, ammonium silicide, ammonium titanium fluoride, sodium fluoride, potassium fluoride, calcium fluoride, lithium fluoride, titanium hydrofluoric acid, zircon hydrofluoric acid, etc. Can be mentioned.

The component containing fluoride ions in the aqueous surface treatment agent is partially or completely lost by forming a coating film made of the aqueous surface treatment agent on the plating layer 2 and then drying the coating film.

The water-based surface treatment agent preferably has a mass ratio (F/Zr) of the mass of fluorine and the mass of zirconium of 0.01 to 2.0. When the above-described mass ratio (F/Zr) is 0.01 or more, the content of fluoride ions in the film 3 can be ensured, and the adhesion and adhesion of the film 3 are improved, which is preferable. When the above-described mass ratio (F/Zr) is 2.0 or less, since zirconium content can be ensured, it is preferable. The mass ratio (F/Zr) is 0.1 to 0.2, more preferably.

The water-based surface treatment agent is obtained by mixing the above-described components in water such as deionized water or distilled water.

Water-based surface treatment agents include alcohols, ketones, cellosolve-based water-soluble solvents, surfactants, antifoaming agents, leveling agents, anti-fungal agents, thickeners, conductive materials for improving weldability, and coloring pigments for improving design, if necessary. You may add a matting material or the like. It is important to add these so as not to deteriorate the quality obtained in the present invention, and the addition amount is less than 5% by mass relative to the total solid content of the aqueous surface treatment liquid, even if the amount is large.

The viscosity of the water-based surface treatment agent is not particularly limited, but the value measured at 25°C is, for example, 1 mPa·s or more and 4 mPa·s or less, preferably 1.2 mPa·s or more and 3 mPa·s or less, more preferably It is 1.5 mPa·s or more and 2 mPa·s or less. If the viscosity of the water-based surface treatment agent is 4 mPa·s or less, the moving speed of the acrylic resin at the time of forming the coating film becomes sufficiently high, and according to the principle described later, the range of the area ratio of the acrylic resin in the upper region A and the center region C. Can be achieved more reliably. Further, when the viscosity of the water-based surface treatment agent is 1 mPa·s or more, coating using a roll coater can be performed with excellent productivity, and the films 3 and 3a can be formed. In addition, the viscosity can be measured using the method described in JIS Z 8803:2011, for example.

Next, in the present embodiment, a coating film is formed by applying the thus obtained aqueous surface treatment agent onto the plating layer 2.

As a method of applying an aqueous surface treatment agent on the plating layer 2, a roll coater is used. In this embodiment, since coating is performed using a roll coater, the film thickness can be easily controlled by adjusting the peripheral speed ratio, and excellent productivity can be obtained.

In addition, when the water-based surface treatment agent is applied onto the plating layer 2, the temperature of the steel sheet 1 when the steel sheet 1 rushes into the roll coater (hereinafter, it may be referred to as ``steel sheet rush temperature''). ) Is preferably 5°C or more and 80°C or less. The structure of the coating film 3 described above is that after applying a water-based surface treatment agent containing an acrylic resin to the surface of the steel plate 1, a part of the acrylic resin moves up and down in the coating film as described later to adsorb the surface, It is formed by interfacial adsorption. When the steel plate rush temperature is above the lower limit of 5°C, the rate of surface adsorption can be sufficiently increased. As a result, the acrylic resin moves a sufficient distance within the time from forming the coating film to be described later to start drying. , The range of the area ratio of the acrylic resin in the upper region A and the central region C can be achieved, and also in the surface structure, the acrylic resin is agglomerated and present in the valleys between the adjacent projections 35 and 35 Crack is suppressed. On the other hand, when the rush temperature of the steel sheet exceeds the upper limit of 80°C, depending on the composition of the water-based surface treatment agent, evaporation of moisture in the water-based surface treatment agent is excessively rapid, resulting in a phenomenon in which small bubble-like expansion or pores occur. A foaming phenomenon occurs. The steel sheet rush temperature is more preferably 10°C or more and 60°C or less, and still more preferably 15°C or more and 40°C or less.

In addition, the temperature of the aqueous surface treatment agent at the time of application of the aqueous surface treatment agent onto the plating layer 2 is not particularly limited, but, for example, 5°C or more and 60°C or less, preferably 10°C or more and 50°C. Hereinafter, it may be more preferably 15°C or more and 40°C or less. When the temperature of the water-based surface treatment agent at the time of application is within the above range, application using a roll coater can be performed with excellent productivity, and the films 3 and 3a can be formed.

The adhesion amount of the water-based surface treatment agent upon application of the water-based surface treatment agent onto the plating layer 2 is not particularly limited, but, for example, 0.03 g/m 2 or more and 3 g/m 2 or less, preferably 0.3 g/m 2 It is 2 g/m 2 or less. The adhesion amount of the aqueous surface treatment agent affects the moving distance in the coating film of the acrylic resin. Therefore, when the adhesion amount is within the above range, the effect of improving the adhesion due to bonding of the surface of the zirconium and the plating layer 2 and the effect of improving the barrier property due to the crosslinked structure of the zirconium and the acrylic resin are further improved. As a result, even more excellent corrosion resistance is obtained. It is possible to prevent the occurrence of cracks caused by containing zirconium in the coatings 3 and 3a, and more excellent corrosion resistance can be obtained.

In this embodiment, after forming the coating film by applying the water-based surface treatment agent on the plating layer 2, until the drying is started, 0.5 seconds or more, preferably 0.5 to 8 seconds, more preferably 0.5 to 4 seconds. , The steel sheet 1 on which the coating film is formed is maintained without drying. When a water-based surface treatment agent containing a zirconium carbonate compound (A) and an acrylic resin (B) is applied on the plating layer 2 containing zinc, as shown below, it is applied on the plating layer 2 to form a coating film. By controlling the time until drying is started after forming, the acrylic resin distribution in the film obtained after drying can be controlled.

When a coating film is formed by applying an acrylic resin and a water-based surface treatment agent containing zirconium, vanadium, phosphorus and cobalt using a roll coater on the plating layer 2 containing zinc, the acrylic resin (B) contained in the coating film is , By the balance of the surface energy, it starts to move to a position that can stably exist in self-alignment. Specifically, the acrylic resin (B) in the coating film moves toward the uppermost surface or lowermost surface that can stably exist. It is the top surface that the acrylic resin (B) in the coating film can exist most stably. For this reason, the movement speed toward the uppermost surface of the acrylic resin (B) in the coating film is faster than the movement speed toward the lowermost surface of the acrylic resin (B) in the coating film.

In addition, the relationship between the time from forming the coating film to the start of drying and the arrangement of the acrylic resin (B) moving in the coating film is the composition of the aqueous surface treatment agent and the acrylic resin (B) in the aqueous surface treatment agent. It changes according to the concentration of However, if the time from forming the coating film to starting drying is 0.5 seconds or more, a sufficient amount of the acrylic resin (B) in the coating film can move toward the top surface by self-alignment. Therefore, the acrylic resin (B) is concentrated on the uppermost surface of the coating film, and the coatings 3 and 3a obtained after drying are as shown in Figs. 1 and 3, in the upper region A in the cross section of the coating film 3 The area ratio of the acrylic resin becomes 80 to 100 area%, and the area ratio of the acrylic resin in the center region C is 5 to 50 area%.

If the time from forming the coating film to starting drying is 3 seconds or more, a sufficient amount of the acrylic resin (B) in the coating film can move toward the top and bottom surfaces by self-alignment. Therefore, the acrylic resin (B) is concentrated on the uppermost surface and the lowermost surface of the coating film, and the film 3 obtained after drying is not only the upper region A in the cross section of the film 3, as shown in FIG. The area ratio of the acrylic resin in the lower region B is also 80 to 100 area%, and the area ratio of the acrylic resin in the central region C is 5 to 50 area%.

When the time from forming the coating film to starting drying is preferably 8 seconds or less, more preferably 4 seconds or less, excellent productivity can be obtained.

The movement of the acrylic resin (B) in the above-described coating film is performed by applying an aqueous surface treatment agent containing acrylic resin, zirconium, vanadium, phosphorus and cobalt on the plating layer 2 containing zinc using a roll coater. It is peculiar to occurring when a coating film is formed.

For example, when a water-based surface treatment agent containing another resin such as a urethane resin instead of an acrylic resin is applied on a plating layer containing zinc, even if the time until the start of drying is within the above range, the top surface of the coating film And the resin is not concentrated on the lowermost surface.

Next, after the coating film is formed, the coating film held for a predetermined time is dried.

By applying the above water-based surface treatment agent using a roll coater and drying it, a plurality of island-like projections are densely formed on the surface by the action shown below by the action shown below.

That is, in the coating film held for a predetermined time, the acrylic resin floats near the top surface. In this state, the coating film is heated and the surface is hardened, so that it is estimated that a plurality of predetermined island-shaped projections will be densely formed.

The temperature at the time of drying the coating film is preferably 60 to 200°C, and more preferably 80 to 180°C, as for the maximum plate temperature (PMT) at the time of drying the coating film. When the maximum attainable plate temperature is 60° C. or higher, moisture, which is the main solvent, is difficult to remain in the coatings 3 and 3a, which is preferable. In addition, when the maximum plate temperature is 200°C or less, decomposition of the acrylic resin 31 does not occur, and thus a problem such as a decrease in corrosion resistance does not occur.

The heating time when drying the coating film can be appropriately determined according to the length of the heating furnace or the line speed of the steel sheet on which the coating film is formed, for example, when heating is performed by a method of passing a steel sheet on which the coating film is formed in a heating furnace.

As a drying method when drying the coating film, induction heating, hot air drying, or drying in a furnace may be mentioned, for example.

Through the above steps, the surface-treated steel sheet 10 according to the first embodiment or the surface-treated steel sheet 20 according to the second embodiment is obtained.

As the coatings 3 and 3a of the surface-treated steel sheets 10 and 20, and the adhesive and top coat layer from which good adhesion is obtained, for example, silicone-based (including acrylic modified, epoxy modified), epoxy-based, acrylic resin-based, phenol And styrene-butadiene rubber-based, urethane-based, vinyl acetate-based, cyanoacrylate-based, and the like.

In addition, the material to be adhered to the coatings 3 and 3a of the surface-treated steel sheets 10 and 20 through an adhesive is not particularly limited, and for example, steel sheet, mortar, float glass, ceramic tile, and MDF (medium density Fiberboard) and the like.

Example

Next, an embodiment of the present invention will be described. In addition, the present invention is not limited to the examples shown below.

1. Manufacturing of surface-treated steel sheet

On the premise that the cross section of the film of the surface-treated steel sheet was mainly observed, a surface-treated steel sheet was manufactured as follows.

First, a steel sheet having a plating layer on both sides shown below was prepared. In addition, a water-based surface treatment agent containing each component shown below at a blending ratio shown in Table 3 was prepared.

The aqueous surface treatment agent was prepared so that the solid content concentration was 15% by mass by sequentially adding each component to a constant amount of deionized water stirred using a propeller stirrer. Carbonic acid and/or ammonia were used as the pH adjuster of the aqueous surface treatment agent. When the aqueous surface treatment agent contains D1 and D2 as the phosphorus compound (P), the mass in terms of P in the aqueous surface treatment agent was prepared so that D1:D2 = 85:15.

(Steel plate with plating layer on both sides)

M1: Hot-dip Zn plating (plating amount 90g/m2)

M2: Hot-dip 11% Al-3% Mg-0.2% Si-Zn plating (plating amount 90 g/m 2)

M3: Electric Zn plating (plating adhesion amount 20g/㎡)

M4: Electric 11% Ni-Zn plating (plating adhesion amount 20g/m²)

M5: Hot-dip 55% Al-1.6% Si-Zn plating (plating adhesion amount 90 g/m 2)

(Ingredients of water-based surface treatment agents)

"Zirconium compound (Zr)"

A1: Potassium zirconium carbonate

A2: ammonium zirconium carbonate

A3: zircon ammonium fluoride

"Acrylic resin"

Styrene (b1), (meth)acrylic acid (b2), (meth) acrylate alkyl ester (b3), and acrylonitrile (b4), which are abbreviated in Table 1, were used in the ratios shown in Table 2, and in Table 2 The copolymers (acrylic resins) of B1 to B17 shown were obtained. Tg at the right end of Table 1 is the polymer glass transition temperature of each monomer. Tg at the right end of Table 2 is the glass transition temperature of the acrylic resins of B1 to B17.

In addition, the content of the acrylic resin in the water-based surface treatment agent in Table 3 is the mass (mass%) with respect to the total solid content of the water-based surface treatment agent.

"Vanadium compound (V)"

C1: vanadium acetylacetonate

C2: vanadium oxyoxalate

"Phosphorus compound (P)"

D1: phosphoric acid

D2: 1-hydroxyethane-1,1-diphosphonic acid

"Cobalt compound (Co)"

E1: Cobalt carbonate

E2: cobalt nitrate

"Fluorine compound (F)"

F1: titanium ammonium fluoride: (NH ₄ ) ₂ TiF ₆

F2: ammonium silicide: (NH ₄ ) ₂ SiF ₆

The steel sheet having a plating layer on both sides described above was degreased by the method shown in (1) below. Thereafter, on both sides of a steel sheet having a plating layer on both sides of the degreased surface, the above-described water-based surface treatment agent is applied to each side by the method shown in (2) to form a coating film, and the coating film is dried by the method shown in (3) below. Then, the surface-treated steel sheets of Examples and Comparative Examples were obtained.

(1) degreasing

Using a degreasing agent (an alkali degreasing agent manufactured by Nihon Parkerizing Co., Ltd., brand name: Fine Cleaner E6406), the steel sheet having a plating layer on both sides was degreased (20 g/L dry bath, 60° C., spray for 10 seconds, spray pressure 50 kPa). . Then, it washed with water for 10 seconds using a spray.

(2) Application of water-based surface treatment agents

The water-based surface treatment agent shown in Table 3 was applied to both surfaces of a steel sheet having a plating layer on both sides of the degreased surface using the coating method shown in Tables 4 and 5, and the coating film retention time shown in Tables 4 and 5 (plating layer on both sides After the water-based surface treatment agent was applied to the steel sheet having a, the time until starting the heating of the steel sheet in the heating furnace) was maintained to form a coating film.

Further, the steel sheet was heated so that the steel sheet temperature (steel sheet rush temperature) when the steel sheet rushes into the roll coater became the temperature shown in Tables 4 and 5. The coating film holding time was adjusted by controlling the conveyance speed of the steel sheet from the roll coater to the heating furnace. In addition, the aqueous surface treatment agent was applied by adjusting the concentration and application amount of the aqueous surface treatment agent so that the Zr adhesion amount shown in Tables 4 and 5 might be obtained. In this case, the viscosity at 25° C. of the aqueous surface treatment agent in each example was in the range of 1.5 to 2 mPa·s. In addition, the temperature of the water-based surface treatment agent itself during application was adjusted as shown in Tables 4 and 5. In addition, in each example, the application amount of the water-based surface treatment agent itself was 0.3 to 2 g/m 2.

In addition, when the intrusion temperature of the steel sheet is 100°C, the water-based surface treatment agent No.3 rapidly evaporated as a result of which water-based surface treatment agent No.3 rapidly evaporated, resulting in a phenomenon in which small expansion or pores in the form of bubbles (so-called forming phenomenon) occurred, resulting in poor appearance. . Therefore, a surface-treated steel sheet having a high-quality coating layer could not be properly manufactured. Therefore, it can be said that the steel plate rush temperature is preferably 80°C or less.

(3) Drying of the coating film

The steel sheet on which the coating film was formed on the plating layer was heated at a maximum plate temperature (PMT) of 150°C while supplying hot air onto the coating film using a warm air circulation type oven (heating furnace) to dry the coating film formed on the plating layer.

2. Evaluation

Each of the following items was investigated about the surface-treated steel sheets of Examples and Comparative Examples thus obtained. The results are shown in Tables 6 to 9.

"Content of V, P, Co, and Zr in the film"

The content (mass%) of V, P (in terms of phosphoric acid) in the coating film (in terms of phosphoric acid), and the content (mass%) of the water-based surface treatment agent shown in Table 3 is regarded as representing the mass ratio with respect to the total solid content in percentage.

「Zr adhesion amount」

It measured with a fluorescence X-ray analyzer (brand name: ZSX-PrimusII (manufactured by Rigaku Corporation)).

"Content of fluoride ions in the film"

Twenty sets of 100 mm×200 mm samples cut out from each surface-treated steel plate were prepared. Next, each sample was immersed in water at 60° C. and 100 mL for 10 minutes. Subsequently, 2000 mL of water immersed in the sample was recovered, concentrated in an evaporator, and analyzed by an ion chromatograph. Using the result, the content (mass%) of the fluoride ion (in terms of F) in the film was calculated.

As a result of calculation in this way, in all of the Examples and Comparative Examples, the content of fluoride ions in the film was 3% by mass or less.

"Area ratio of acrylic resin"

A carbon film was vapor-deposited as a protective film on the surface of each surface-treated steel sheet, and a carbon film of several micrometers was formed into a film using FIB (focused ion beam processing apparatus, SMI3050SE: manufactured by Hitachi High-Tech Science). Thereafter, microsampling was performed using FIB at an acceleration voltage of 30 kV (finish processing; 5 kV), and this was made into a thin film to obtain a film cross-section sample.

Each film cross-section sample was observed using a TEM or SEM having an EDS (energy dispersive X-ray spectroscopy), and EDS analysis (element mapping) was performed at each of three locations to obtain a detection element map. The obtained detection element map was divided into 100 cells (10×10), and the C component and other elements were binarized using the contrast of the image, and the area ratio of the C component in each region of the film cross section It was calculated as the area ratio of the resin.

In addition, infrared spectral analysis and pyrolysis GC-MS (gas chromatograph-mass spectrometry) analysis were performed on the film peeled off by acid treatment from each surface-treated steel sheet. And the result of analysis from the attribution of the observed absorption derived from the resin component in the infrared absorption spectrum of the film obtained by infrared spectroscopy, and the analysis result of pyrolysis GC-MS confirmed that the C component in the film was an acrylic resin.

The area ratio of the calculated acrylic resin was evaluated as follows.

<Area from the surface to a thickness of 1/5 of the film thickness (upper region A)>

1: 0 area% or more and less than 80 area%

2: 80 area% or more and 90 area% or less

3: 90 area% or more and 100 area% or less

<The area from the center of the film thickness to the surface side to a thickness of 1/10 and the area from the center of the film thickness to the thickness of the plating layer to the thickness of 1/10 (center area C)>

1: 0 area% or more and less than 5 area%

2: 5 area% or more and 50 area% or less (excluding 10 area% or more and 40 area% or less)

3: 10 area% or more and 40 area% or less

4: More than 50 area% and 100 area% or less

<Area from the interface with the plating layer to a thickness of 1/5 of the film thickness (lower region B)>

1: 0 area% or more and less than 80 area%

2: 80 area% or more and 90 area% or less

3: 90 area% or more and 100 area% or less

<Overall film cross section>

1: 0 area% or more and less than 20 area%

2: 20 area% or more and 60 area% or less (excluding 30 area% or more and 50 area% or less)

3: 30 area% or more and 50 area% or less

4: More than 60 area% and 100 area% or less

「Corrosion resistance」

A flat plate test piece and an Ericsson processed test piece having a height of 7 mm and subjected to the Ericsson processing were prepared. Each test piece was subjected to a salt spray test conforming to JIS Z 2371 until a predetermined time. The evaluation criteria for corrosion resistance are shown below.

Flat plate test piece (240 hours after salt spray test)

4: 5% or less

3: White bluish more than 5% and 15% or less

2: More than 15% white and 30% or less

1: more than 30% white rust

Eriksen processed test piece (72 hours after salt spray test)

4: 15% or less

3: more than 15% white and less than 30%

2: More than 30% white and less than 50%

1: more than 50% white rust

「My black metamorphosis」

Using a constant temperature and humidity tester, the appearance after leaving the test piece to stand for 144 hours in an atmosphere of 70°C x RH85% was visually observed. The evaluation criteria for blackening resistance are shown below.

5: No change at all

4: Little change was observed

3: A slight discoloration is observed at the tip

2: Slight discoloration is observed

1: obvious discoloration is confirmed

「Adhesion with adhesive」

Using various adhesives, the adhesion between the surface-treated steel sheets was performed by the following (evaluation method 1) and (evaluation method 2). The adhesive is shown below.

A: Epoxy system (manufactured by Konishi, E2300J)

B: Acrylic (Denki Chemical Co., Ltd., Hard Rock 8)

C: Silicon (manufactured by Toray Dow Corning, PV8303)

D: Silicon (manufactured by Semedine, PM210)

E: Silicone type (manufactured by Semedine, Super X No.8008)

F: phenolic (manufactured by Semedine, 110)

G: Urethane (made by Semedine, UM700)

H: vinyl acetate system (manufactured by Konishi, CH18)

I: Chloroprene rubber system (manufactured by Semedine, 575F)

(Evaluation method 1)

An adhesive was applied between two test pieces (25±0.5 mm×100±0.5 mm×1.6 mm thick) made of a surface-treated steel sheet, and a lab shear test body having an area of 25±0.5 mm×12.5±0.5 mm on the bonded portion was prepared. Was produced. About the lab shear test body which was cured for a predetermined time after applying the adhesive, it evaluated by the evaluation criteria of the tensile shear load and the cohesive failure rate shown below.

(Evaluation method 2)

The same test body as that for evaluating the primary adhesiveness in (Evaluation Method 1) was evaluated according to the evaluation criteria of the tensile shear load and cohesive failure rate shown below after a predetermined time elapsed at a temperature of 85°C and a humidity of 85%.

(Evaluation criteria for tensile shear load (Criteria X))

For each lab shear test body, a tensile shear test was performed at a tensile speed of 100 mm/min and a room temperature of 25°C. And, the ratio of the tensile shear load of each lap shear test body and the tensile shear load of the untreated material (a test body using a steel plate having a plating layer on both sides before forming a film instead of a surface-treated steel sheet) (tensile shear load of the test body/no The tensile shear load of the treated material) was calculated and evaluated. The evaluation criteria of the tensile shear load ratio are shown below.

4: 1.1 or higher

3: greater than 1.0 to less than 1.1

2: 1.0 (equivalent to untreated material)

1: less than 1.0

(Evaluation criterion of aggregation destruction rate (standard Y))

The cohesive failure rate was evaluated by comparing the residual area (cohesive failure rate) of the adhesive in each lab shear test body after the tensile shear test with the cohesive failure rate in the untreated material after the tensile shear test. The evaluation criteria of the cohesive failure rate are shown below.

4: The residual area of the adhesive is clearly increased compared to the untreated material

3: The residual area of the adhesive is increased compared to the untreated material

2: The remaining area of the adhesive is equal to that of the untreated material

1: The remaining area of the adhesive is lower than that of the untreated material

「Adhesion with the upper layer」

The test plate was coated under the following conditions, and a coating film adhesion test was performed. The results are shown in Tables 6 and 7.

(Painting conditions)

Painting conditions Paint: Kansai Paint Co., Ltd. Amylac #1000 (registered trademark) (white paint)

Coating method: Bar coating method

Baking drying conditions: 140℃, 20 minutes

Coating thickness: 25㎛

The evaluation method is as follows.

(Coating film adhesion test)

The test plate was immersed in boiling water for 2 hours and allowed to stand for one day and night, and then, a square, 100 checkerboard eyes having one side of 1 mm were cut with an NT cutter, and a peel test with an adhesive tape was performed, and the number of peeling of the coating film was evaluated. The evaluation criteria are shown below.

4: The number of peelings is less than 1

3: The number of peelings is 1 or more and less than 10

2: The number of peelings is 10 or more and less than 50

1: The number of peelings is 50 or more

As shown in Tables 6 to 10, all of the surface-treated steel sheets according to Examples 1 to 68, which are examples of the present invention, had sufficient corrosion resistance and blackening resistance, and good adhesion to adhesives.

In contrast, as shown in Tables 6 to 10, in the surface-treated steel sheets according to Comparative Examples 1 to 5 having a film not containing any of acrylic resin, zirconium, vanadium, phosphorus and cobalt, the upper region A The area ratio of the acrylic resin was less than 80 area%. For this reason, in Comparative Examples 1 to 7, adhesion to the adhesive was insufficient. In particular, in Comparative Example 2, since the film did not contain an acrylic resin component, cracks in the surface structure were remarkably generated, and the adhesion was poor.

Further, in Comparative Example 5 having a film containing no cobalt, the blackening resistance was insufficient.

In addition, in the surface-treated steel sheet according to Comparative Example 6, in which the surface treatment agent was applied and maintained for less than 0.5 seconds and then heated, the area ratio of the acrylic resin in the upper region A was less than 80 area%, and cracks in the surface structure. Since the suppression was insufficient, the adhesion to the top coat layer and the adhesion to the adhesive were insufficient. In addition, even in the surface-treated steel sheet according to Comparative Example 6 in which the steel sheet intrusion temperature was less than 5°C, the area ratio of the acrylic resin in the upper region A was less than 80 area%, and the crack suppression in the surface structure was insufficient. The adhesion to the layer and the adhesion to the adhesive were insufficient.

The cross section of the surface-treated steel sheet of each Example and Comparative Example was observed using a field emission transmission electron microscope (FE-TEM) (manufactured by Nippon Denshi Corporation).

4 is a TEM image of a cross section of a surface-treated steel sheet according to Example 42.

In the TEM image of the cross section of the surface-treated steel sheet according to Example 42 shown in FIG. 4, a coating made of a plurality of particulate white portions (acrylic resin) and a gray inhibitor phase was observed on the surface, and the uppermost and lowermost surfaces were observed. The concentration of the acrylic resin is higher than that of the acrylic resin in the entire film.

In the surface-treated steel sheet according to Example 42, the area ratio of the acrylic resin in the upper area A is 80 area% or more, the area rate of the acrylic resin in the lower area B is 90 area% or more, and the area of the acrylic resin in the center area C The ratio was 5 area% or more and 50 area% or less.

Further, an enlarged TEM image of the cross section of the surface-treated steel sheet according to Example 42 is shown in Fig. 17, and Fig. 18 is a SEM image of the surface of the surface-treated steel sheet according to Example 42. As shown in Fig. 17, in the range in the thickness direction from the upper region A including the central region C to the lower region B, the bridge portion of the acrylic resin to which the acrylic resin is connected in a column shape is observed (in the drawing, the arrow portion Reference). These bridge portions correspond to the protrusions indicated by arrows in Fig. 18 and the valleys between the protrusions. In the film 3, the acrylic resin is agglomerated like a column, and the bridge portion that supports the portion between the protrusions 35 and the valleys of the protrusions 35 on the surface suppresses the occurrence of cracks, the adhesion to the adhesive, and the top coat. It is thought that the adhesion to the layer was improved.

5 is a TEM image of a cross section of a surface-treated steel sheet according to Example 41.

In the TEM image of the cross section of the surface-treated steel sheet according to Example 41 shown in FIG. 5, a coating formed of a plurality of particulate white portions (acrylic resin) and a gray inhibitor phase was observed on the surface, and the uppermost acrylic resin was observed. The concentration is higher than that of the acrylic resin in the entire film.

In the surface-treated steel sheet according to Example 41, the area ratio of the acrylic resin in the upper area A is 80 area% or more, the area rate of the acrylic resin in the lower area B is less than 80 area%, and the area of the acrylic resin in the center area C The ratio was 5 area% or more and 50 area% or less.

6 is a TEM image of a cross section of a surface-treated steel sheet according to Example 3. FIG.

In the TEM image of the cross section of the surface-treated steel sheet according to Example 3 shown in Fig. 6, a film made of a plurality of particulate white portions (acrylic resin) and a gray inhibitor phase was observed on the surface, and the uppermost acrylic resin was observed. The concentration is higher than that of the acrylic resin in the entire film.

In the surface-treated steel sheet according to Example 3, the area ratio of the acrylic resin in the upper area A is 80 area% or more, the area rate of the acrylic resin in the lower area B is less than 80 area%, and the area of the acrylic resin in the center area C The ratio was 5 area% or more and 50 area% or less.

3. Manufacturing of surface-treated steel sheet

Next, in order to observe the surface state of the surface-treated steel sheet, a surface-treated steel sheet was produced and evaluated as follows. First, a steel sheet having a plating layer on both sides described above was degreased by the method shown in (4) below. Thereafter, on both surfaces of a steel sheet having a plating layer on both sides of the degreased surface, the above water-based surface treatment agent was applied by the method shown in (5) to form a coating film, and the coating film was dried by the method shown in (6). , To obtain a surface-treated steel sheet according to each Example and Comparative Example.

(4) degreasing

Using a degreasing agent (an alkali degreasing agent manufactured by Nihon Parkerizing Co., Ltd., brand name: Fine Cleaner E6406), the steel sheet having a plating layer on both sides was degreased (20 g/L dry bath, 60° C., spray for 10 seconds, spray pressure 50 kPa). . Then, it washed with water for 10 seconds using a spray.

(5) Application of water-based surface treatment agents

A coating film was formed by applying a water-based surface treatment agent shown in Table 3 to both surfaces of a steel sheet having a plating layer on both sides of the degreased sheet using a roll coater. The aqueous surface treatment agent was applied by adjusting the concentration and application amount of the aqueous surface treatment agent so that the Zr adhesion amount shown in Tables 11 and 12 might be obtained. In addition, the temperature of the water-based surface treatment agent itself at the time of application was adjusted as shown in Tables 11 and 12. In addition, in each example, the application amount of the water-based surface treatment agent itself was 0.3 to 2 g/m 2.

In addition, when the rush temperature of the steel sheet is 100° C., as a result of rapid evaporation of moisture from the aqueous surface treatment agent, small expansion or pores in the form of bubbles (so-called forming phenomenon) occur, resulting in poor appearance. Therefore, a surface-treated steel sheet having a high-quality coating layer could not be properly manufactured. Therefore, it can be said that the steel plate rush temperature is preferably 80°C or less.

In addition, at this time, the steel sheet was heated so that the steel sheet temperature (steel sheet rush temperature) when the steel sheet rushes into the roll coater became the temperature shown in Tables 11 and 12. The coating film holding time was adjusted by controlling the conveyance speed of the steel sheet from the roll coater to the heating furnace. In addition, at this time, the viscosity at 25°C of the aqueous surface treatment agent in each example was in the range of 1.5 to 2 mPa·s.

(6) Drying of the coating film

The steel sheet on which the coating film was formed on the plating layer was heated at 150° C. of the highest plate temperature (PMT) using an induction heating (IH) device to dry the coating film formed on the plating layer.

4. Evaluation

For the surface-treated steel sheets of Examples and Comparative Examples thus obtained, the above-described "2. Each item of "evaluation" was investigated. In addition, each of the following items was evaluated. The results are shown in Tables 13 to 15. In addition, about the evaluation of "adhesiveness with an adhesive", about the adhesive shown in said A, evaluation was performed typically.

「The length of the protrusion on the surface of the film」

Using a field emission scanning electron microscope (FE-SEM) (manufactured by Hitachi Seisakusho), the surface of the surface-treated steel sheet of Example 112 was observed at a magnification of 5000 times, and the image shown in FIG. 7 was obtained. On the obtained rectangular image (long side about 13 µm, short side about 9.5 µm), three imaginary straight lines consisting of a diagonal line of the image and a straight line parallel to the long side through the intersection of the diagonal lines were drawn. And with respect to all the protrusions which the virtual straight line traversed, the length of the virtual straight line traversing each protrusion was measured, the average value was calculated, and it was set as the length of the protrusion. In addition, the minimum and maximum values among the lengths of all the projections measured to calculate the length of the projection were investigated.

As a result, the length of the protrusion of Example 112 was 0.87 µm, the minimum value described above was 0.15 µm, and the maximum value described above was 1.62 µm.

Further, in the same manner as the surface-treated steel sheet of Example 112, the surface of the surface-treated steel sheet of Example 109 was observed, and an image shown in FIG. 8 was obtained. Using the obtained image, in the same manner as in Example 112, the length of the projection and the minimum and maximum values of the lengths of all the projections measured to calculate the length of the projection were examined.

As a result, the length of the protrusion of Example 109 was 0.35 µm, the minimum value was 0.15 µm, and the maximum value was 0.92 µm.

In all Examples and Comparative Examples except Example 109 and Example 112, in the same manner as in the surface-treated steel sheet of Example 112, the surface of the surface-treated steel sheet was observed, and using the obtained image, the projections were carried out in the same manner as in Example 112. The minimum and maximum values were investigated among the lengths of and the lengths of all the projections measured to calculate the length of the projections. The results are shown in Tables 13 to 15.

「Roughness of projections on the surface of the film」

The arithmetic mean roughness (Ra), the maximum cross-sectional height of the roughness curve (Rt), and the root mean square roughness (Rq) of the surface in a rectangular region with a side of 1 μm were measured under atomic force microscope (AFM) (Digital Inst. Manufacturing) was used. The results are shown in Tables 13 to 15.

"Zirconium distribution in the film"

By using an EPMA (electron beam microanalyzer) to analyze the film from the surface, the concentration of zirconium in the ``area between adjacent protrusions'' and ``area in which protrusions are formed'' in the film is obtained, It evaluated according to the following criteria. The results are shown in Tables 13 to 15.

Y: The concentration of zirconium in the region between adjacent projections is less than the concentration of zirconium in the region in which the projections are formed.

N: The concentration of zirconium in the region between adjacent projections is equal to or greater than the concentration of zirconium in the region in which the projections are formed.

``Components between adjacent projections''

The surface of the film was analyzed using EPMA (electron beam microanalyzer), and the distribution of the carbon component detected by the above analysis was regarded as the distribution of the acrylic resin, and evaluated according to the following criteria. The results are shown in Tables 13 to 15.

Y: The concentration of the carbon component in the region between the adjacent projections exceeds the concentration of the carbon component in the region in which the projections are formed.

N: The concentration of the carbon component in the region between adjacent projections is equal to or less than the concentration of the carbon component in the region in which the projections are formed.

In addition, infrared spectral analysis and pyrolysis GC-MS (gas chromatograph-mass spectrometry) analysis were performed on the film peeled off by acid treatment from each surface-treated steel sheet, and the infrared absorption spectrum of the film obtained by infrared spectral analysis was analyzed. From the results of analysis from the attribution of the observed absorption derived from the resin component and the analysis results of pyrolysis GC-MS, it was confirmed that the carbon component in each film was derived from an acrylic resin.

As shown in Tables 13 to 15, all of the surface-treated steel sheets according to Examples 68 to 133, which are examples of the present invention, had good corrosion resistance, adhesion to adhesives, and adhesion to top coat layers.

In contrast, as shown in Tables 13 to 15, in the surface-treated steel sheets according to Comparative Examples 8 to 13 having a film not containing any of acrylic resin, zirconium, vanadium, phosphorus and cobalt, corrosion resistance or adhesive and The adhesiveness of was insufficient.

For Examples 69 to 133, in the region from the surface in the cross section of the film to the thickness of 1/5 of the film thickness (upper region A), the area ratio of the acrylic resin is 80 to 100 area%, and the film thickness center A region (center area C2) consisting of a region from the surface side to a thickness of 1/10 a film thickness (upper center region C1) and a region from the film thickness center to the plating layer side to a thickness of 1/10 (lower center region C2) In region C), it was confirmed that the area ratio of the acrylic resin was 5 to 50 area%. Further, on the surface of the film, a plurality of irregular and island-like projections in plan view were densely formed, and cracks were suppressed.

In the surface-treated steel sheets according to Comparative Examples 8 to 12 having a film not containing any of acrylic resin, zirconium, vanadium, phosphorus, and cobalt, the area ratio of the acrylic resin in the upper region A was less than 80% by area. For this reason, in Comparative Examples 8 to 12, adhesion to the adhesive was insufficient. In particular, since Comparative Example 9 did not contain an acrylic resin component, cracks in the surface structure were remarkably generated and adhesion was poor. Further, in Comparative Example 12 having a coating containing no cobalt, the blackening resistance was insufficient.

In addition, in the surface-treated steel sheet according to Comparative Example 13 in which the steel sheet intrusion temperature was less than 5°C, the area ratio of the acrylic resin in the upper region A was less than 80 area%, and the crack suppression in the surface structure was insufficient. The adhesion to the layer and the adhesion to the adhesive were insufficient.

9 is an SEM image of the surface of a surface-treated steel sheet according to Example 70, and FIG. 10 is an AFM image. 11 is an SEM image of the surface of a surface-treated steel sheet according to Example 111, and FIG. 12 is an AFM image.

As shown in Figs. 9 to 12, on the surface of the film in the surface-treated steel sheets of Examples 70 and 111, a plurality of irregular and island-shaped projections in plan view were formed in a dense manner.

13 is an SEM image of Comparative Example 9, and FIG. 14 is an AFM image. The film of Comparative Example 9 does not contain an acrylic resin. For this reason, as shown in Figs. 13 and 14, on the surface of the film in the surface-treated steel sheet of Comparative Example 9, irregular and island-like projections were not formed in plan view. As shown in FIG. 13, cracks (cracks) reaching the plating layer existed on the surface of the film in the surface-treated steel sheet of Comparative Example 9.

15 is an SEM image of a surface-treated steel sheet according to Comparative Example 8, and FIG. 16 is an AFM image. The coating of the surface-treated steel sheet according to Comparative Example 8 does not contain zirconium. For this reason, as shown in Figs. 15 and 16, on the surface of the film in the surface-treated steel sheet according to Comparative Example 8, irregular and island-like projections were not formed in plan view.

In the above, preferred embodiments of the present invention have been described, but the present invention is not limited to the above-described embodiments. That is, it is understood that other forms or various modifications that can be conceived by those skilled in the art within the scope of the invention described in the claims are also within the technical scope of the present invention.

1: steel plate
2: plating layer
3, 3a: film
10, 20: surface-treated steel plate
31: acrylic resin
32: Inhibitor Award
33: surface
34: interface
35: protrusion
L: virtual straight line

Claims (13)

It has a steel plate, a plated layer containing zinc formed on the steel plate, and a film formed on the plated layer,
The film contains acrylic resin, zirconium, vanadium, phosphorus and cobalt,
In a region from the surface in the cross section of the film to a thickness of 1/5 of the film thickness, the area ratio of the acrylic resin is 80 to 100 area%,
The area ratio of the acrylic resin in a region consisting of a region from the center of the film thickness of the film to a thickness of 1/10 to the surface side and a region from the center of the film thickness to a thickness of 1/10 to the plating layer side Surface-treated steel sheet having 5 to 50% by area. The method of claim 1,
On the surface of the film, there are a plurality of island-like projections in plan view,
In plan view, when three or more imaginary straight lines having a length of 10 μm or more and extending in an arbitrary direction are drawn at an arbitrary position on the surface of the film, the imaginary straight line is a portion that crosses the protrusion. When the average value of the length of the line segment is defined as the length of the protrusion, the length of the protrusion is 0.1 to 5.0 μm. The method of claim 2,
The arithmetic mean roughness (Ra) of the surface of the film in a rectangular area with one side of 1 μm is 5 to 50 nm, the maximum cross-sectional height (Rt) of the roughness curve is 50 to 500 nm, and the root mean square roughness (Rq) A surface-treated steel sheet of 10 to 100 nm. The method according to claim 2 or 3,
A surface-treated steel sheet in which the concentration of the zirconium in a region between adjacent projections in the film is lower than that of the zirconium in a region in which the projections are formed. The method according to claim 2 or 3,
A surface-treated steel sheet in which the concentration of the acrylic resin in a region between the adjacent projections in the film is higher than that of the acrylic resin in a region in which the projections are formed. The method according to any one of claims 1 to 3,
In the film, a mass ratio (V/Zr) of the mass of the vanadium and the mass of the zirconium is 0.07 to 0.69,
The mass ratio (P/Zr) of the mass of the phosphorus and the mass of the zirconium is 0.04 to 0.58,
The surface-treated steel sheet having a mass ratio (Co/Zr) of the mass of cobalt and the mass of zirconium is 0.005 to 0.08. The method according to any one of claims 1 to 3,
A surface-treated steel sheet containing 4 to 400 mg/m 2 of zirconium in terms of metal in the film. The method according to any one of claims 1 to 3,
A surface-treated steel sheet having an area ratio of 20 to 60 area% of the acrylic resin in the cross section of the film. The method according to any one of claims 1 to 3,
The surface-treated steel sheet, wherein the plating layer is composed of at least one of 60% by mass or less of Al, 10% by mass or less of Mg, and 2% by mass or less of Si, zinc and impurities. The method according to any one of claims 1 to 3,
The said acrylic resin is 15 to 25 mass% of styrene, 1 to 10 mass% of acrylic acid or methacrylic acid, 40 to 58 mass% of acrylate alkyl ester or methacrylate alkyl ester, and 20 to 38 mass% of acrylic It is a copolymer of nitrile, the glass transition temperature of the acrylic resin is -12 to 24 ℃ surface-treated steel sheet. The method according to any one of claims 1 to 3,
The surface-treated steel sheet in which the film contains 5% by mass or less of fluoride ions. It is the manufacturing method of the surface-treated steel sheet in any one of Claims 1-3,
A step of forming a plating layer containing zinc on a steel sheet, and
Applying an acrylic resin, zirconium, vanadium, phosphorus, and a water-based surface treatment agent containing cobalt on the plating layer using a roll coater to form a coating film;
A step of holding the coating film for at least 0.5 seconds until drying of the coating film is started after the coating film is formed;
The process of drying the coating film
A method for producing a surface-treated steel sheet having. The method of claim 12,
In the step of applying the water-based surface treatment agent, the temperature of the steel sheet when the steel sheet rushes into the roll coater is 5°C or more and 80°C or less.

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